Studies are continuing on interactions of cardiac glycosides with red cell membranes. The action of ouabain on the outside of human red cells is reflected in the metabolism of glycolytic intermediates which contain P31; these interactions will be studied with the aid of a nuclear magnetic resonance spectrometer. We plan to use the temperature jump device to continue our studies of the kinetics of phloretin interaction (in the microsecond range) with lipid vesicles and red cell membranes. Our studies on the thermodynamics of partition of small solutes between an aqueous medium and lipid vesicles have indicated that solute dimerization within the vesicles should be an important process. We plan to look for direct evidence of amide dimerization in lipid vesicles, both by optical means, using excimers formed from pyrene butyramide and by nuclear magnetic resonance using N15 labeled amides. We also hope to combine the thermodynamic data from our partition studies with kinetic data on membrane permeation to specify the energy barriers that control passive membrane transport of nonelectrolytes. BIBLIOGRAPHIC REFERENCES: Poznansky, M.J., S. Tong and A.K. Solomon. 1975. Permeability of spherical lipid bilayers to a homologous series of short-chain monoamides. Fed. Proc. 34:326. Abstract. Poznansky, J.J., S. Tong, P.C. White, J.M. Milgram and A.K. Solomon. 1976. Nonelectrolyte diffusion across lipid bilayer systems. J. Gen. Physiol. 67:45-66.